Photosensitive elements which can be used in image-reproduction processes are well-known in the graphics arts industry. Such elements are exposed to actinic radiation through an image-bearing transparency, such as a color separation transparency, and developed to produce an image which is either positive or negative with respect to the transparency used. Positive-working elements produce an image which is a duplicate of the transparency through which they are exposed. Negative-working elements produce an image that is the reverse of the transparency through which they are exposed. After imagewise exposure, the photosensitive elements may be developed by washout of soluble image areas, toning tacky image areas with a colorant, peeling apart photoadherent layers, or combinations of these techniques. A series of images may be combined to form a color proof. A useful reference for color proofing methods is Principles of Color Proofing, by Michael H. Bruno, GAMA Communications, Salem,. N.H., 1986.
In Cohen and Fan, U.S. Pat. No. 4,282,308, there is described a photosensitive element which is capable of producing reverse, colored images by a dry process without the need for toning with a colorant. The element comprises, in order from top to bottom, a strippable cover sheet, a photoadherent layer containing a colorant, a tacky essentially nonphotosensitive elastomeric layer, and a support. After imagewise exposure to actinic radiation through the cover sheet, the element can be peeled apart by peeling off the cover sheet with the exposed areas of the colored photoadherent layer adhered thereto. The unexposed areas of the colored photoadherent layer remain on the supported elastomeric layer. When the imagewise exposure is through a negative transparency, and the exposed element is peeled apart, a positive image is obtained on the peeled-off cover sheet and a negative image is obtained on the supported elastomeric layer. Imagewise exposure through a positive transparency, followed by peeling apart of the element, yields a negative image on the peeled-off cover sheet and a positive image on the supported elastomeric layer. However, these tacky, essentially nonphotosensitive, elastomeric layer-containing elements result in high peel force peel-apart systems.
A need exists for a photosensitive element comprised of layers which have a low peel force and the required adhesion balance so the element can be effectively developed using peel-apart development.